To　investigate　the　fire　resistance　of　L-section　fireproof　board　and　thin　concrete　encased　steel　(L-FBTCES)　column,　four　columns　were　tested　under　constant　axial　compression　and　ISO-834　standard　fire,　varying　the　load　ratio　and　concrete　encasement　thickness.　The　failure　modes,　thermal　response,　deformation　response,　and　fire　resistance　time　were　obtained.　The　thermal　response　curve　of　the　steel　exhibited　three　stages,　and　the　maximum　temperature　of　the　steel　was　below　600　degrees　C　during　the　test.　The　fire　resistance　time　for　all　specimens　exceeded　120　minutes.　The　resistance　time　decreased　with　the　increase　of　the　load　ratio　and　slightly　increased　with　the　increase　of　the　concrete　encasement.　The　thermo-mechanical　coupling　models　were　established,　and　the　numerical　parametrical　analysis　was　conducted.　Based　on　the　existing　specifications　for　composite　columns　and　considering　the　adjusted　load　ratio　and　fireproof　board　thickness,　a　modified　calculation　method　for　L-FBTCES　columns　was　proposed　and　validated　by　the　numerical　analysis　results.